The installation of wall-to-wall carpeting typically involves stretching the carpet to obtain a smooth, flat installation. This generally entails installing tack strips around the perimeter of the area to be covered with carpet adjacent to the walls of the area. The carpet is then rolled out in the room, usually over some padding, cut and seamed. One side of the carpet is attached to the tack strip along one side of a room and then stretched to the other side using conventional carpet stretchers which exert hundreds of pounds of force on the carpet. This process is intended to remove any wrinkles or creases in the carpeting, resulting in a flat, safe and visually appealing carpet installation.
Three specific requirements have historically confronted the art of carpet seaming in a stretched carpet installation. First, if a process is to be utilized in conjunction with stretch carpet installation, the seam must be sufficiently durable and permanent to withstand the forces imparted in the carpet stretching process. Second, for obvious cosmetic purposes, the seam should be as close as possible to being invisible. Third, the process should be as simple and economical as possible.
Existing methods require a trade-off between these requirements. For example, creating a seam by sewing two abutting edges of adjoining carpet pieces together, as described in, e.g., U.S. Pat. Nos. 3,440,981, 3,457,884, and 3,499,402, produces a seam of high strength that is able to withstand stretching during installation, but is very costly and time-consuming to produce. If done too quickly, or by a person not sufficiently skilled, the joined edges could be improperly aligned or carpet pile caught by the thread, making the seam visible and unsightly. This has proven inimical to the efficient and economical installation of seamed carpeting.
Early attempts at avoiding the significant costs of sewing seams included the use of adhesives and special fasteners. One technique involves the use of sheet metal strips having sharp prongs which penetrate the carpet backing from the bottom side. They are most often formed from stamping through a single piece of sheet metal to form pointed metal prongs extending out to engage the underside of the carpeting transverse to a seam area. See, e.g., Reinhard, U.S. Pat. Nos. 2,552,114; Finch, 2,673,169, Milnes, 2,890,145 and Krantz, 3,413,678. The sheet metal strip from which such prongs are stamped have significant longitudinal strength traversing a seam. However, this seaming method includes a number of problems. The metal prongs cannot, alone, securely hold the carpet backing. The entire strip lies uniformly below the carpeting backing. Consequently, any force of the tension in the process of carpet stretching is transmitted in a line along the metal strips beneath the line of the carpet backing. This tension can give rise to carpet peaking. One solution is to glue or affix the metal strip to the floor (see, e.g., Krantz, U.S. Pat. No. 3,413,678); however, a glue down process is incompatible with stretched-in carpet installation. Another problem is that the prongs, whether at right angles from the metal strip or bent more sharply, are straight and cannot prevent the carpet from rising up and off. As prongs must be kept short, to prevent injury to persons walking over the seam, the problem is exacerbated. One solution is to use adhesive with the protruding prongs to glue the prongs into the carpet backing (See, e.g., Reinhard and Krantz above); however, this requires additional time and labor.
Finally, when prongs are stamped out of sheet metal or like material, the prongs are sharp not only on the point piercing the carpet backing, but also on the edges which engage the fibers of the carpet backing to hold the carpet in place. This can result in cutting of the carpet fibers and backing which surround the metal prong, resulting in the gradual loosening of the carpet seam.
Mechanical solutions, such as sewing and the use of mechanical strip fasteners, have given way in recent years to seaming using hot melt adhesive seaming tape. This method avoids the significant time and effort burdens imposed by sewing, avoids the unreliability of mechanical strip fasteners, and enables seaming to be conducted by relatively unskilled workers. In this process, a strip of tape having a layer of hot melt adhesive is centered under the seam with the layer of hot melt adhesive facing up. An iron, or other suitable implement, is used to melt the hot melt adhesive, and the carpet backing is pushed into the molten hot melt adhesive with the two edges abutting. The adhesive quickly sets, forming a permanent seam. This method is disclosed by, e.g., U.S. Pat. Nos. 3,972,768, 4,097,445, and 4,416,713. When initially introduced, this method produced satisfactory results. However, over time, as carpet mills sought to reduce the costs of manufacturing and changed the structure of carpet backings, hot melt carpet seaming produced two major problems: seam peaking and profiling.
Seam "peaking" is a common problem in stretched carpet installation. See, e.g., U.S. Pat. No. 4,919,743 (Johnson et al., 1990). Seam peaking occurs when the abutting edges of the carpet at a seam form a relatively sharp ridge. Seam peak ridges are unsightly and typically result in excessive wear at the seam. Seam peaking may result from the use of excessive heat during seam sealing, or from the tension which is put on the carpet during stretching. Johnson '743 and U.S. Pat. No. 4,749,433 (Johnson et al., 1988) disclose the use of enhanced width seaming tape. However, such tape is expensive to use and may not eliminate entirely the peaking problem.
Many efforts have been made to combat seam peaking, including the enhanced width tape disclosed by Johnson, as well as tapes having steel rods, bars or wires which are placed transversely to the seam line. These solutions do not work in every instance, with all kinds of carpets. Indeed, some of the most expensive carpets, such as Berber carpets, continue to exhibit peaking even after the above methods have been used to prevent peaking.
Seam "profiling" is another problem which is encountered in stretched carpet installations. Profiling occurs where the carpet surface which is directly over the seaming tape bulges during or following stretching to produce a longitudinal mound along the seam which is typically as wide as the seaming tape which is used. Thus, if an installer uses a wider tape, such as a 6" tape, to combat seam peaking, the seam peaking may be avoided, but the installer ends up with a "profile" which is typically about 6" wide all along the seam. The cause of profiling is not known with certainty, but it appears that the absorption of hot melt adhesive into the backing of the carpet reduces the flexibility of the backing, causing bulging when the carpet is stretched.
Accordingly, the need exists for a carpet seaming technique and apparatus that is capable of producing a strong reliable permanent seam, able to substantially reduce or avoid peaking, profiling and other unacceptable cosmetic anomalies, and be reasonably inexpensive, quick and easy to use.